1. Field of the Invention
This invention relates to the manufacture of plastics bags, e.g., for use as bin liners.
2. The Prior Art
It is well known to manufacture plastic bags by extruding a tube of polyethylene, expanding the tube to reduce the thickness of the polyethylene film, flattening the tube and then heat sealing and severing or perforating the tube across its width. The heat seals form the bottoms of the bags. If the bags are initially divided by transverse perforation lines, a series of bags can be wound into a roll for supply to a customer who can tear individual bags off the roll as required for use. In order to reduce the size of the machinery demanded and also to improve the strength of the welded seals, it is well known to fold the polyethylene tubing prior to the heat sealing operation. An especially effective seal is obtained if the tubing is folded as described in GB-A-1584746. According to this method the sides of the tubing are folded inwardly to form longitudinal gussets which reach in substantially to the longitudinal centre line of the layflat tubing, and the gusseted tubing is then folded in half onto itself about the longitudinal centre line. When folded in this way, eight layers of film become welded together over substantially the whole length of the heat seal subsequently produced, and a strong seal is obtained. However, this folding method is not suitable for the manufacture of rolls of interconnected bags formed, by appropriate cutting, with handles at the bag mouths. Such handles may be desirable for tying closed the bag after it has been filled, e.g., with refuse. Because the gusseted tubing is folded in half, handles formed at the side edges, i.e., at the folds of the gussets, will be superimposed at the same side of the folded tube, and the resulting string of bags can not be satisfactorily wound into a roll.